Methods and apparatus for loading a very long instruction word memory

ABSTRACT

The ManArray processor is a scalable indirect VLIW array processor that defines two preferred architectures for indirect VLIW memories. One approach treats the VIM as one composite block of memory using one common address interface to access any VLIW stored in the VIM. The second approach treats the VIM as made up of multiple smaller VIMs each individually associated with the functional units and each individually addressable for loading and reading during XV execution. The VIM memories, contained in each processing element (PE), are accessible by the same type of LV and XV Short Instruction Words (SIWs) as in a single processor instantiation of the indirect VLIW architecture. In the ManArray architecture, the control processor, also called a sequence processor (SP), fetches the instructions from the SIW memory and dispatches them to itself and the PEs. By using the LV instruction, VLIWs can be loaded into VIMs in the SP and the PEs. Since the LV instruction is supplied by the SP through the instruction stream, when VLIWs are being loaded into any VIM no other processing takes place. In addition, as defined in the ManArray architecture, when the SP is processing SIWs, such as control and other sequential code, the PE array is not executing any instructions. Techniques are provided herein to independently load the VIMs concurrent with SIW or iVLIW execution on the SP or on the PEs thereby allowing the load latency to be hidden by the computation.

RELATED APPLICATIONS

The present invention claims the benefit of U.S. Provisional applicationSer. No. 60/171,911 entitled “Methods and Apparatus for Loading a VeryLong Instruction Word Memory” and filed Dec. 23, 1999 which isincorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to improvements in parallelprocessing, and more particularly to techniques for the loading of verylong instruction word (VLIW) memory in an indirect VLIW processor whichallows the load latency to be hidden by computation.

BACKGROUND OF THE INVENTION

An indirect VLIW processor is organized with a VLIW memory (VIM) that isseparate from its short instruction word (SIW) memory. The VIM isdefined for an instruction set architecture by way of specific SIWs thatcontrol the loading and execution of the VLIWs stored in the VIM. Forexample, a load VLIW (LV) instruction is defined which acts as a setupcontrol delimiter instruction for the processor logic. The LVinstruction specifies the VIM address where a VLIW is to be stored andthe number of SIWs which follow the LV instruction that are to be storedat the specified VIM address in VLIW fashion. Another special SIW is theexecute VLIW (XV) instruction. The XV instruction causes a VLIW to beread out of VIM at the XV specified address.

The ManArray processor defines two preferred architectures for indirectVLIW memories. One approach treats the VIM as one composite block ofmemory using one common address interface to access any VLIW stored inthe VIM. The second approach treats the VIM as made up of multiplesmaller memories each individually associated with the functional unitsand each individually addressable for loading and reading during XVexecution. It will be recognized that improved techniques loading ofVLIW memory will be highly desirable.

SUMMARY OF THE PRESENT INVENTION

The present invention covers techniques to independently load the VIMsconcurrent with SIW or iVLIW execution on the SP or on the PEs therebyallowing the load latency to be hidden by the computation. The ManArrayprocessor which is a scalable indirect VLIW array processor is thepresently preferred processor for implementing these concepts. The VIMmemories, contained in each processing element (PE), are accessible bythe same type of LV and XV SIWs as in a single processor instantiationof the indirect VLIW architecture. In the ManArray architecture thecontrol processor, also called the sequence processor (SP), fetches theinstructions from the SIW memory and dispatches them to itself and thePEs. By using the LV instruction, VLIWs can be loaded into VIMs in theSP and the PEs. Since the LV instruction is supplied by the SP throughthe instruction stream, when VLIWs are being loaded into any VIM noother processing takes place. In addition, as defined in the ManArrayarchitecture, when the SP is processing SIWs, such as control and othersequential code, the PE array is not executing any instructions. Withthe techniques presented herein, the latency to load the VIM can behidden by the computation.

A more complete understanding of the present invention, as well as otherfeatures and advantages of the invention will be apparent from thefollowing Detailed Description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates aspects of ManArray indirect VLIW instruction memoryin accordance with the present invention;

FIG. 2 illustrates the basic iVLIW Data Path;

FIG. 3 illustrates a five slot iVLIW with an expanded view of the ALUslot;

FIG. 4A illustrates an LV1 Load/Modify VLIW Instruction;

FIG. 4B illustrates an XV1 Execute VLIW Instruction;

FIG. 4C illustrates an LV2 Load/Modify Instruction;

FIG. 4D illustrates an XV2 Execute VLIW Instruction;

FIG. 5 illustrates aspects of an iVLIW LV1/XV1 pipeline apparatus;

FIG. 6 illustrates aspects of an iVLIW LV2/XV2 pipeline apparatus;

FIG. 7 illustrates a Type-1 VIM DMA apparatus;

FIG. 8 illustrates a Type-2 VIM DMA apparatus; and

FIG. 9 illustrates a Type-2 VIM DMA-ALU portion apparatus.

DETAILED DESCRIPTION

The present invention may be applicable to a variety of processing andarray designs; however, an exemplary and presently preferredarchitecture for use in conjunction with the present invention is theManArray® architecture. Further details of a presently preferredManArray core, architecture, and instructions for use in conjunctionwith the present invention are found in U.S. patent application Ser. No.08/885,310 filed Jun. 30, 1997, now U.S. Pat. No. 6,023,753, U.S. patentapplication Ser. No. 08/949,122 filed Oct. 10, 1997, now U.S. Pat. No.6,167,502, U.S. patent application Ser. No. 09/169,255 filed Oct. 9,1998, now U.S. Pat. No. 6,343,356, U.S. patent application Ser. No.09/169,256 filed Oct. 9, 1998, now U.S. Pat. No. 6,167,501, U.S. patentapplication Ser. No. 09/169,072, filed Oct. 9, 1998, now U.S. Pat. No.6,219,776, U.S. patent application Ser. No. 09/187,539 filed Nov. 6,1998, now U.S. Pat. No. 6,151,668, U.S. patent application Ser. No.09/205,588 filed Dec. 4, 1998, now U.S. Pat. No. 6,173,389, U.S. patentapplication Ser. No. 09/215,081 filed Dec. 18, 1998, now U.S. Pat. No.6,101,592, U.S. patent application Ser. No. 09/228,374 filed Jan. 12,1999 now U.S. Pat. No. 6,216,223, U.S. patent application Ser. No.09/238,446 filed Jan. 28, 1999, now U.S. Pat. No. 6,366,999, U.S. patentapplication Ser. No. 09/267,570 filed Mar. 12, 1999, now U.S. Pat. No.6,446,190, U.S. patent application Ser. No. 09/337,839 filed Jun. 22,1999,U.S. patent application Ser. No. 09/350,191 filed Jul. 9, 1999, nowU.S. Pat. No. 6,356,994, U.S. patent application Ser. No. 09/422,015filed Oct. 21, 1999 now U.S. Pat. No. 6,408,382, U.S. patent applicationSer. No. 09/432,705 filed Nov. 2, 1999 entitled “Methods and Apparatusfor Improved Motion Estimation for Video Encoding”, U.S. patentapplication Ser. No. 09/471,217 filed Dec. 23, 1999 entitled “Methodsand Apparatus for Providing Data Transfer Control”, U.S. patentapplication Ser. No. 09/472,372 filed Dec. 23, 1999 now U.S. Pat. No.6,256,683, U.S. patent application Ser. No. 09/596,103 filed Jun. 16,2000, now U.S. Pat. No. 6,397,324, U.S. patent application Ser. No.09/598,567 entitled “Methods and Apparatus for Improved Efficiency inPipeline Simulation and Emulation” filed Jun. 21, 2000, U.S. patentapplication Ser. No. 09/598,564 filed Jun. 21, 2000, now U.S. Pat. No.6,622,238, U.S. patent application Ser. No. 09/598,566 entitled “Methodsand Apparatus for Generalized Event Detection and Action Specificationin a Processor” filed Jun. 21, 2000, and U.S. patent application Ser.No. 09/598,084 filed Jun. 21, 2000, now U.S. Pat. No. 6,654,870, U.S.patent application Ser. No. 09/599,980 entitled “Methods and Apparatusfor Parallel Processing Utilizing a Manifold Array (ManArray)Architecture and Instruction Syntax” filed Jun. 22, 2000, all of whichare assigned to the assignee of the present invention and incorporatedby reference herein in their entirety.

In a preferred embodiment of the present invention, a ManArray 2×2 iVLIWsingle instruction multiple data stream (SIMD) processor 100 illustratedin FIG. 1 is employed. Processor 100 includes a controller sequenceprocessor (SP) combined with a processing element-0 (PE0) SP/PE0 101 asdescribed in further detail in U.S. patent application Ser. No.09/169,072 entitled “Methods and Apparatus for Dynamic Merging an ArrayController with an Array Processing Element”. Three additional PEs 151,153, and 155 are used to describe the DMA and other techniques ofloading of VIM memories. The SP/PE0 101 contains a fetch controller 103to allow the fetching of SIWs from a 32-bit instruction memory 105. Thefetch controller 103 provides the typical functions needed in aprogrammable processor such as a program counter (PC), a branchcapability, event point loop operations (for further details of suchoperations see U.S. Provisional application Ser. No. 60/140,245 entitled“Methods and Apparatus for Generalized Event Detection and ActionSpecification in a Processor” filed Jun. 21, 1999), and support forinterrupts. It also provides the instruction memory control which couldinclude an instruction cache if needed by an application. In addition,the SIW I-Fetch controller 103 dispatches 32-bit SIWs to the other PEsin the system by means of a 32-bit instruction bus 102.

In this exemplary system, common elements are used throughout tosimplify the explanation, although actual implementations are notlimited to this restriction. For example, the execution units 131 in thecombined SP/PE0 101 can be separated into a set of execution unitsoptimized for the control function, for example, fixed point executionunits, and the PE0 as well as the other PEs can be optimized for afloating point application. For the purposes of the present description,it is assumed that the execution units 131 are of the same type in theSP/PE0 101 and the PEs 151, 153 and 155. In a similar manner, SP/PE0 andthe other PEs use a five instruction slot iVLIW architecture whichcontains a VLIW memory (VIM) 109 and an instruction decode and VIMcontroller function unit 107 which receives instructions as dispatchedfrom the SP/PE0's I-Fetch unit 103 and generates the VIMaddresses-and-control signals 108 required to access the iVLIWs storedin the VIM 109. The iVLIWs are identified by the letters SLAMD thatreference the Store(S), Load (L), ALU (A), MAU (M), and DSU (D)execution units. The loading of the iVLIWs is described in furtherdetail in U.S. patent application Ser. No. 09/187,539 entitled “Methodsand Apparatus for Efficient Synchronous MIMD Operations with iVLIWPE-to-PE Communication”. Also contained in the SP/PE0 and the other PEsis a common PE configurable register file (CRF) 127 which is describedin further detail in U.S. patent application Ser. No. 09/169,255entitled “Method and Apparatus for Dynamic Instruction ControlledReconfiguration Register File with Extended Precision”.

Due to the combined nature of the SP/PE0 101, the data memory interfacecontroller 125 must handle the data processing needs of both the SPcontroller, with SP data in memory 121, and PE0, with PE0 data in memory123. The SP/PE0 controller 125 also is the source of the data that issent over the 32-bit or 64-bit broadcast data bus 126. The other PEs,151, 153, and 155 contain common physical data memory units 123′, 123″,and 123′″ though the data stored in them is generally different asrequired by the local processing done on each PE. The interface to thesePE data memories is also a common design in PEs 1, 2, and 3 andindicated by PE local memory and data bus interface logic 157, 157′ and157″. Interconnecting the PEs for data transfer communications is acluster switch 171 described in further detail in U.S. patentapplication Ser. Nos. 08/885,310 entitled “Manifold Array Processor”,08/949,122 entitled “Methods and Apparatus for Manifold ArrayProcessing”, and 09/169,256 entitled “Methods and Apparatus for ManArrayPE-to-PE Switch Control”. The interface to a host processor, otherperipheral devices, external memory or the like can be done in manyways. The primary mechanism shown for completeness is contained in a DMAcontrol unit 181 that provides a scalable ManArray data bus 183 thatconnects to devices and interface units external to the ManArray core.The DMA control unit 181 provides the data flow and bus arbitrationmechanisms needed for these external devices to interface to theManArray core memories including the VIM via the multiplexed businterface symbolically represented by line 185 and internal DMAinterfaces 173, 175, 177, and 179. All of the above noted patents areassigned to the assignee of the present invention and incorporatedherein by reference in their entirety.

Indirect Very Long Instruction Word (iVLIW) Architecture

Each SP/PE0 101 and each PE 151, 153, 155 in the ManArray architectureshown in FIG. 1 contains a quantity of iVLIW memory (VIM) 109. Each VIM109 contains space to hold multiple VLIW Instructions, and eachaddressable VIM location is capable of storing up to eight shortinstruction words (SIWs). Current implementations allow each iVLIWinstruction to contain up to five simplex instructions: one in each ofthe store unit (SU), load unit (LU), arithmetic logic unit (ALU),multiply-accumulate unit (MAU), and data-select unit (DSU). For example,an iVLIW instruction at some VIM address “i” contains the fiveinstructions SLAMD as indicated in the VIM 109 of FIG. 1.

FIG. 2 shows the basic iVLIW instruction flow execution path 200 inwhich a fetched instruction is stored in an instruction register 20which is connected to a VIM load and store control functional unit 22.The VIM load and store control functional unit provides the interfacesignals to a VIM 24. The output of the VIM 24 is pipelined to an iVLIWregister 26.

FIG. 3 illustrates a five slot iVLIW VIM 300 with N entries. Theexpanded ALU slot view indicates a 32-bit storage space, thoughdepending upon the implementation the specific number of bits requiredto represent an instruction can vary.

iVLIW instructions can be loaded into an array of PE VIMs collectively,or, by using special instructions to mask a PE or PEs, each PE VIM canbe loaded individually. The iVLIW instructions in VIM are accessed forexecution through the execute VLIW (XV) instruction, which when executedas a single instruction causes the simultaneous execution of the simplexinstructions located at a specified VIM memory address.

Two basic instruction types are used to load/modify iVLIW memories, andto execute iVLIW instructions. They are:

1. Load/Modify VLIW Memory Address (LV1) instruction 400 shown in FIG.4A, and

2. Execute VLIW (XV1) instruction 425 shown in FIG. 4B.

As shown in FIG. 4A, the LV1 instruction 400 is for 32-bit encodings asshown in illustrative encoding block 410. A presently preferredsyntax/operation for this instruction is shown in syntax/operation block420. The LV1 instruction 400 is used to load and/or disable individualinstruction slots of the specified SP or PE VLIW Memory (VIM). The VIMaddress is computed as the sum of the base VIM address register Vb (V0or V1) plus an unsigned 8-bit offset VIMOFFS shown in bits 0-7, theblock of bits 411 of encoding block 410 of FIG. 4A. The VIM address mustbe in the valid range for the hardware configuration otherwise theoperation of this instruction is undefined.

Any combination of individual instruction slots may be disabled via thedisable slot parameter ′d={SLAMD}, where S=store unit (SU), L=load unit(LU), A=arithmetic logic unit (ALU), M=multiply-accumulate unit (MAU),and D=data select unit (DSU). A blank ′d=′parameter does not disable anyslots. An instruction loaded into a slot marked by the disable slotparameter remains disabled when loaded.

The number of instructions to be loaded are specified utilizing anInstrCnt parameter. For the present implementation, valid values are0-5. As specified by this parameter, the number instructions nextfollowing the LV1 are loaded into the specified VIM address. Furtheroperational description of the load VLIW instruction can be found inU.S. patent application Ser. No. 09/187,539.

The XV1 instruction 425 shown in FIG. 4B is also for 32-bit encoding asshown in illustrative encoding block 430. A presently preferredsyntax/operation for this instruction is shown in syntax/operation block435. The XV1 instruction 425 is one of a control group of instructionsdefined by group field bits 30 and 31 of encoding block 410, and is usedto execute individual instruction slots of the specified SP's or PE's,as specified by bit 29, VLIW memory (VIM). The VIM address is computedas the sum of a base VIM address register Vb (V0 or V1) plus an unsigned8-bit offset VIMOFFS shown in bits 0-7, the block of bits 431 inencoding block 430 of FIG. 4B. The VIM address must be in the validrange for the hardware configuration otherwise the operation of thisinstruction is undefined. Further operational description of the executeVLIW instruction is also found in the above mentioned application.

LV1 and XV1 operations in accordance with the present invention arediscussed with reference to FIG. 5 where aspects of the iVLIW load andfetch pipeline are described in connection with an iVLIW system 500.Among its other aspects, FIG. 5 shows a selection mechanism for allowingselection of instructions out of VIM memory. A fetched instruction isloaded into instruction register 1 (IR1) 510. Register 510 correspondsgenerally with instruction register 20 of FIG. 2. The output of IR1 ispredecoded by predecoder 512 early in the pipeline cycle prior toloading values into instruction register 2 (IR2) 514. When theinstruction in IR1 is a load iVLIW (LV1) with a non-zero instructioncount, the predecoder 512 generates the LVc1 control signals 515, whichare used to set up the LV1 operation cycle. The VIM address 511 iscalculated by use of the specified Vb register 502 added by adder 504with the offset value included in the LV1 instruction via path 503. Theresulting VIM address 511 is stored in register 506 and passed throughmultiplexer 508 to address the VIM 516. VIM 516 corresponds generally toVIM 109 of FIG. 1.

Register 506 is required to hold the VIM address 507 during the LV1operations. The VIM address 511 and LV1 control state allows the loadingof the instructions received after the LV1 instruction into the VIM 516.At the end of the cycle in which the LV1 was received, the disable bits10-17 shown in FIG. 4A are loaded into a d-bits register 518 for usewhen loading instructions into the VIM 516. Upon receipt of the nextinstruction in IR1 510, which is to be loaded into VIM 516, theappropriate control signal is generated depending upon the instructiontype, Storec1 519, Loadc1 521, ALUc1 523, MAUc1 525, or DSUc1 527. Theoperation of predecoder 512 is based upon a simple decoding of the groupbits (bits 30 and 31 of FIGS. 4A-D) which define the instruction typeshown in FIGS. 4A-D, a Load/Store bit, and the unit field (bits 27 and28) of an ALU, MAU, or DSU type instruction. By using this predecodestep, the instruction in IR1 510 can be loaded into VIM 516 in theproper functional unit position.

For example, when an ADD instruction included in the LV1 list ofinstructions is received into IR1 510, it can be determined by thepredecoder 512 that the ADD instruction is to be loaded into the ALUInstruction slot 520 in VIM 516. In addition, the appropriate d-bit 531for that functional slot position is loaded into bit-31 of that slot.The loaded d-bit occupies one of the group code bit positions from theoriginal instruction.

Upon receipt of an XV1 instruction in IR1 510, the VIM address 511 iscalculated by use of the specified Vb register 502 added by adder 504with the offset value included in the XV1 instruction via path 503. Theresulting VIM Address 507 is passed through multiplexer 508 to addressthe VIM. The iVLIW at the specified address is read out of the VIM 516and passes through the multiplexers 530, 532, 534, 536, and 538, to theIR2 registers 514. As an alternative to minimize the read VIM accesstiming critical path, the output of the VIM can be latched into aregister whose output is passed through a multiplexer prior to thedecode state logic.

For XV1 execution, an IR2MUX1 control signal 533 in conjunction with thepredecode XVc1 control signal 517 cause all the IR2 multiplexers, 530,532, 534, 536, and 538, to select the VIM output paths, 541, 543, 545,547, and 549. At this point, the five individual decode and executionstages of the pipeline, 540, 542, 544, 546, and 548, are completed insynchrony providing iVLIW parallel execution performance. To allow asingle 32-bit instruction to execute by itself in the PE or SP, thebypass VIM path 535 is shown. For example, when a simplex ADDinstruction is received into IR1 510 for parallel array execution, thepredecoder 512 generates the IR2MUX1 533 control signal, which inconjunction with the instruction type predecode signal 523 in the caseof an ADD, and lack of an XV 517 or LV 515 active control signal, causesthe ALU multiplexer 534 to select the bypass path 535.

An alternative VIM configuration exists for within slot compressionmechanism. This mechanism is described in further detail in U.S. patentapplication Ser. No. 09/205,558. In this approach, the VIM is divided upinto separate VIM sections each associated with corresponding functionaldecode-and-execute units. Each of the VIMs' address maps are dividedinto multiple 4-bit addressable sections as governed by an offset fieldincluded in a new version of the execute iVLIW instruction, XV2, with aseparate offset that can be specified for each VIM slot section. ThisVIM configuration and XV2 addressing option provides the ability toindependently select instructions within each VIM slot 4-bit addressrange. By doing this, duplicate SIWs within the 16 addressable iVLIWrange can be eliminated providing greater packing of SIWs within thecomposite VIM.

The XV2 instruction is similar to the XV1 instruction in that it is usedto modify, enable/disable sub-iVLIW instructions, and indirectly executeiVLIW instructions in the SP and PEs but does so in a different way thanthe XV1 instruction. For the XV2 instruction, it is still assumed thatthe iVLIWs have been loaded into this new partitioned VIM by use of anew version of the load VLIW instruction, LV2 455 shown in FIG. 4C. TheLV2 encoding 450 consists of a CtrlOp field, bits 25-28, that representthe LV2 instruction opcode. A load instruction bit-23 specifies if atleast one instruction is to be loaded or if the disable d-bit for thespecified address is to be loaded. Bit-22 is the disable d-bit that isloaded. Bits 18-21 specify that up to 16 instructions are to be loadedin the specified functional unit's VIM, as specified by bits 15-17,beginning at the address specified by one of the Vb registeredaddresses, as selected by bit-9, plus the VIMOFFS offset address, bits0-7. Presently preferred syntax/operation details are shown insyntax/operation table 460.

An XV2 instruction 475 is shown in FIG. 4D. The encoding format 470includes new bit fields as follows. UAF field bits 23 and 24 are notoptional on XV2 instruction 475 and must be specified with each XV2 use.The VIM base register selection Vb is established by bit 20, and thefive offset fields are store VIM offset (SOFS) bits 16-19, load VIMoffset (LOFS) bits 12-15, ALU VIM offset (AOFS) bits 8-11, MAU VIMoffset (MOFS) bits 4-7, and DSU VIM offset (DOFS) bits 0-3. Thepresently preferred syntax/operation is shown in syntax/operation table480.

Referring to FIG. 6, VIM 616 consists of multiple independent memoryunits each associated with their functional decode and execute units.Independent addressing logic is provided for each slot VIM. Asillustrated in FIG. 6, each VIM entry preferably consists of five SIWslots (one per execution unit) and associated with each SIW slot areadditional state bits, of which 5 are shown (one d-bit per slot).Included among the five execution units are a store unit 640 associatedwith store instruction VIM 620, load unit 642 associated with loadinstruction VIM 622, an arithmetic-logic unit (ALU) 644 associated withALU instruction VIM 624, a multiply accumulate unit (MAU) 646 associatedwith MAU instruction VIM 626, and a data select unit (DSU) 648associated with DSU instruction VIM 628.

The FIG. 6 VIM address adder functional blocks, as exemplified by ALUVIM address adder 604, are different than the adder functional block 504as shown in FIG. 5 in order to support the VIM address incrementcapability required by the load VLIW-2 (LV2) instruction 455 of FIG. 4Cas described in the syntax/operation block 460. This capability allowsthe instructions following the LV2 instruction to be loaded at:

(V[01 ]+VIMOFFS)[UnitVIM]←1^(st) Instruction following LV2

(V[01 ]+VIMOFFS+1)[UnitVIM]←2^(nd) Instruction following LV2

(V[01 ]+VIMOFFS+InstrCnt)[UnitVIM]←(InstrCnt)^(th) Instruction followingLV2 The instruction count parameter InstrCnt is a binary coded number, 0thru F, that represents from 1 to 16 instructions that can be loadedinto up to 16 consecutive UnitVIM locations.

The five state d-bits 621, 623, 625, 627, and 629 are LV-loaded disablebits for the instruction slots that indicate either: the SIW slot isavailable-for-execution or it is not-available-for-execution. A binaryvalue suffices to distinguish between the two states. An instructionslot with its d-bit set to the not-available-for-execution state isinterpreted as an NOP (no-operation) instruction by the execution unit.In addition, the appropriate d-bit for that functional slot position isloaded into bit-31 of that slot.

ManArray DMA Background

The ManArray PEs 101, 151, 153, 155 of FIG. 1 each have their own localmemories 123, 123′, 123″, and 123′″, respectively. These PE localmemories are accessible from a program through use of the PE load andstore instructions. PE local memories may also be accessed by the DMAcontroller for data transfers to and from other system memories. The DMAcontroller 181 accesses a PE local memory bank only when the PE does notrequire access to the particular port requested by the DMA. This accessapproach is termed “cycle borrowing” since the processor is neverstalled for DMA access. PE0 which shares its load and store units withthe SP behaves like any other PE with respect to its local memoryaccesses.

Type-1 VIM DMA

FIG. 7 depicts a type-1 VIM DMA apparatus 700 with type-1 VIM 708similar to the type-1 VIM apparatus 500 and VIM 516 shown in FIG. 5, butwith the addition of DMA control apparatus as shown in FIG. 7. Thetype-1 VIM DMA apparatus represents an extension to the basic DMA memoryinterface provided in each PE. The “cycle borrowing” technique is alsoused in VIM DMA operations. The preferred VIM 708 is a two port memoryallowing simultaneous read and write accesses. It is anticipated that inapplications where performance is not critical or where simultaneousread and write accesses are deemed not necessary that a single sharedread/write port VIM can be used. In the two port design, each portrequires its own address and write or read control signals. A writeaddress 731 is sourced from multiplexer 736 since the VIM can be loadedfrom either instruction path 727 with LV1 instructions or from DMAoperations on path 729. Read address 725 is only accessed from theinstruction side under control of XV1 instructions. The DMA operationconsists of a “data” packet made up of SIWs that begin with an LV1 typeinstruction, followed by the SIWs constituting the VLIW to be loaded atthe address specified in the LV1 instruction. Multiple VLIW packets canbe loaded into VIM during a single VIM DMA request with each packetoptionally varying in size depending upon the number of SIWs containedin each VLIW.

Operation is as follows. The “data” packet, when the DMA operationbegins, is transferred beginning with the LV1 “data” item over the32-bit DMA bus 715 and stored into DMA Register 1 (DR1) 710. The output717 of DR1 is provided to the VIM controller 722 which provides “cycleborrow” control to the DMA interface. The received LV1 instructioncauses the correct Vx base address register to be selected via path 726and adder 724 adds the base Vx value to the offset found in the receivedLV1 OFFSET field 719 which is labeled Doffset. The resultant sum isstored in register 730 for later use. A programmer can use the two Vxbase address registers V0 and V1 to aid this process where one, sayregister V0, can be set up for the instruction iVLIW usage and theother, register V1, for DMA base address use. The DMA packet willcontinue sending the next LV1 SIWs one at a time through DR1 710 to beloaded into the correct slot position DMA register for the SU 712, LU714, ALU 716, MAU 718, and DSU 720. At this point, the full VLIW “data”packet has been loaded into the PEs and the VIM controller 722 can allowthe VLIW to be loaded at the LV1 specified address as long as theinstruction side does not take priority. The VIM controller 722 selectsthe multiplexer 736 to the DMA VIM address 729 and selects themultiplexers 750-758 to the VMA registers and in a single cycle the fullVLIW is then loaded into the VIM. The DMA interface is then allowed toproceed with the next VLIW “data” packet if there is one.

Type-2 VIM DMA

FIG. 8 illustrates a type-2 VIM DMA apparatus 800 with a type-2 VIM 808similar to the type-2 VIM apparatus 600 and VIM 616 shown in FIG. 6, butwith the addition of DMA apparatus as shown in FIG. 8. In FIG. 8, theVIM is partitioned into a VIM section per functional unit each withduplicate controls and each operated in the same manner. Due to thecomplexity of FIG. 8, the ALU VIM portion and its associated controlshave been broken out and shown in further detail in FIG. 9 for furtherdetailed discussion of its operation. In FIG. 9 the assembly 900processes the instruction 909 and utilizes a DMA 915 interface and ALUVIM 903 and control inputs from a controls section of the type-2 VIMsystem. The type-2 VIM DMA apparatus represents an extension to thebasic DMA memory interface provided in each PE. The “cycle borrowing”technique is also used in VIM DMA operations. Each preferred VIMportion, for example VIM portion 903, is a two port memory allowingsimultaneous read and write accesses. It is anticipated that inapplications where performance is not critical or where simultaneousread and write accesses are deemed not necessary a single sharedread/write port VIM can be used.

In the two port design, each port requires its own address and write orread control signals. The write address 931 is sourced from multiplexer936 since the VIM can be loaded from either instruction path 927 withLV2 instructions or from DMA operations on path 929. The read address925 is only accessed from the instruction side under control of XV2instructions. DMA operation consists of a “data” packet made up of SIWsthat begin with a LV2 type instruction, followed by the SIWsconstituting the specified functional VIM portion to be loaded at theaddress specified in the LV2 instruction. The type-2 VIM differs fromthe type-1 VIM in that type-2 functional VIM portions are loaded up to16 locations at a time while the type-1 VIM loads a single VIM addresswith the up to 5 SIWs constituting the single VLIW. The type-1 VIM DMAalso buffered up a whole VLIW line of SIWs prior to loading the fullVLIW in a single cycle to the specified VLIW address. In the type-2 VIMapparatus, it is important to note that the whole block of SIWs for eachVIM portion gets loaded prior to that range of VIM addresses which areused by the XV2 instructions. This load priority is necessary becausethe XV2 instruction allows SIWs to be selected from the differentftunctional VIM portions at different VIM addresses in parallel. The DMAsubsystem would be scheduled to transfer a whole block of VIM data forall functional VIM portions. In this manner, the programmer candetermine that when the type-2 DMA operation is complete all portions ofthe VIM are available for program use. The type-2 VIM DMA operationwould transfer a single SIW at a time and not buffer up a full VLIW setof multiple SIWs as was done in the type-1 VIM DMA operation.

When this type 2 VIM DMA operation begins, the “data” packet istransferred beginning with the LV2 “data” item over the 32-bit DMA bus915 and stored into DMA register 1 (DR1) 910. The output 917 of DRi isprovided to VIM controller 922 which provides “cycle borrow” control tothe DMA interface. The received LV2 instruction causes the correct Vxbase address register to be selected via path 926 and adder 924 adds thebase Vx value to the offset found in the received LV2 unit VIM offsetfield 945 (FIG. 4C bits 7-0 for the ALU defined by bits 17-15). Theresultant sum is stored in register 930 for later use. A programmer canuse the two Vx base address registers to aid this process where one, sayregister V0, can be set up for the instruction iVLIW usage and theother, register V1, for DMA base address use. The DMA packet willcontinue sending the next LV2 SIWs one at a time through DRI 910 to beloaded into the ALU VIM portion. For each SIW received at 910, the SIWis loaded directly into the ALU VIM portion under control of the VIMcontrol 922 at the LV2 instruction specified address for the first SIWand then incrementally as long as the instruction side does not takepriority. The DMA VIM control logic automatically increments the VIMaddress in preparation for the next SIW received on the DMA interface.The VIM controller 922 selects multiplexer 936 for the DMA VIM address929 and selects the multiplexer 954 to the DR1 register output 917 andin a single cycle the SIW is then loaded into the ALU VIM 903. The DMAinterface is then allowed to proceed with the next SIW “data” item ofthe DMA packet if there is one. It is noted that if the “data” packet iscommon to multiple PEs, the multiple PEs' functional VIM portions can beloaded in parallel and in synchronism. The DMA operation continues foreach functional partition of the full Type-2 VIM apparatus.

Alternate VIM Load Mechanisms via SP or PE Instructions

Two alternate methods for loading VIMs (other than DMA):

(1) SP/PE Store to Special Purpose Register (SSPR) instructions to aspecified VIM Port SPR address; and

(2) an SP/PE Load instruction which targets the VPORT MRF register.

Both of these approaches have the following features:

Different LOAD (memory) addresses allow different VLIWs to be loadedinto each VIM to support synchronous multiple instruction multiple data(SMIMD) processing setup.

It is not necessary to use instruction memory for LV instructions.

LV instructions can be placed into PE local memories by DMA using bothchannels for reducing overall VIM load time. DMA can place LVinstructions into PE memories in background and VIMs can be loaded in ¼the time required currently when application needs them.

These approaches also allow the SP or the PEs to reload VIMs whileprocessing other instructions by use of the VLIW architecture.

Another method for loading VIMs in parallel is via PE SSPR instructions.The PE SSPR instruction is basically a variation of the STOREinstruction. The SSPR instruction targets a particular address. VLIWinstructions (LV followed by a list of instructions) can be loaded intoPE memories via DMA, then a LOAD to a PE or SP register followed by anSSPR instruction to a VPORT PE SPR address can be used to load PE VIMsin parallel. This approach has several benefits.

The Load/SSPR data (LV and following instructions) would normally betargeting the instruction register of each PE in the present ManArrayarchitecture, thereby conflicting with subsequent instructions in thepipe. This conflict is solved by providing an alternate decode register(same as with DMA) which would allow an LV instruction with followingdata to be decoded in parallel with any other instruction received fromthe instruction bus. With XVs, this approach requires a dual port VIM.In this approach, loads/stores in an XV can be used to load VIMs witheffective throughput of 4 instructions per cycle.

Interrupts must be disabled while VIMs are being loaded. Currently,interrupts are not allowed while processing an LV sequence. In thepresent architecture, the SP knows what is going on since it decodes theLV instruction. In this approach, there is no signal for PEs writing toa special “VIM load port” using a particular PE SPR address. Onesolution is to add a signal that is asserted whenever a value is writtento the VIM Write Port SPR address of any PE or whenever the VPORT inputregister (of any PE) has data in it for loading into VIM.

While the present invention has been disclosed in a presently preferredcontext, it will be recognized that the present teachings may be adaptedto a variety of contexts consistent with this disclosure and the claimsthat follow.

We claim:
 1. A very long instruction word (VLIW) memory (VIM) directmemory access (DMA) apparatus comprising: a single VLIW memory (VIM)having a plurality of memory locations, each memory location having aplurality of functional unit positions, each functional unit positionfor storing a corresponding instruction; a DMA interface; a DMA verylong instruction word (VLIW) line buffer for receiving a data packethaving a plurality of instructions through the DMA interface; and asingle cycle write VLIW line controller controlling the loading of eachreceived instruction of the plurality of instructions into itscorresponding functional unit position of the plurality of functionalunit positions.
 2. The apparatus of claim 1 wherein the VIM is a twoport memory allowing simultaneous read and write accesses.
 3. Theapparatus of claim 2 wherein said controller provides each of the twoports its own address and read or write control signals.
 4. Theapparatus of claim 1 wherein said line buffer temporarily stores thedata packet comprising a load/modify VLIW memory address (LV1)instruction and a plurality of short instruction words (SIWs)constituting a VLIW to be loaded at an address specified in the LV1instruction.
 5. The apparatus of claim 1 wherein said controllerprovides cycle borrow control to the DMA interface.
 6. A method forloading very long instruction word (VLIW) memory (VIM) through a directmemory access (DMA) controller, said method comprising: providing asingle VLIW memory (VIM) having a plurality of memory locations, eachmemory location having a plurality of functional unit positions, eachfunctional unit position for storing a corresponding instruction;receiving a data packet having a plurality of instructions; and loadingeach received instruction of the plurality of instructions to acorresponding functional unit position within a memory locationutilizing a single cycle write VLIW line controller during a single VIMDMA request.
 7. The method of claim 6 wherein the VIM is a two portmemory allowing simultaneous read and write accesses, and the methodfurther comprises the step of providing each of the two ports its ownaddress and read or write control signals.
 8. The method of claim 6further comprising the step of temporarily storing in a line buffer aplurality of data packets comprising a load/modify VLIW memory address(LV1) instruction and a plurality of short instruction words (SIWs)constituting a VLIW to be loaded at an address specified in the LV1instruction.
 9. The method of claim 6 further comprising the step ofutilizing said single cycle write VLIW line controller to provide cycleborrow control to a DMA interface.
 10. The apparatus of claim 1 furthercomprising a base address register storing a base address, and whereinthe VLIW line controller loads the instruction words into VIM at anaddress determined utilizing the base address and an offset valuecontained in a load instruction.
 11. The apparatus of claim 1 furthercomprising a plurality of base address registers, each base addressstoring a base address, and wherein the VLIW line controller loads theinstruction words into VIM at an address determined utilizing both anoffset value contained in a load instruction and one of the base addressregisters specified by the load instruction.
 12. The method of claim 6further comprising: storing a base address in a base address register,wherein the VLIW line controller loads the instruction words into VIM atan address determined utilizing both an offset value contained in a loadinstruction and one of the base address registers specified by the loadinstruction.
 13. The method of claim 6 further comprising: storing baseaddresses each of a plurality of base address registers, wherein theVLIW line controller loads the instruction words into VIM at an addressdetermined utilizing both an offset value contained in a loadinstruction and one of the base address registers specified by the loadinstruction.